1. Field of the Invention
The invention concerns an electric machine with a single pole winding and a soft magnetic body that is composed of pole segments, as well as a process for its production. Electric machines, in particular electrically commutated (EC) [EC] external rotors of small capacity show advantageously individually spooled poles. Single pole windings avoid overlapping of conductors of different phases and, therefore, can be spooled very compactly.
2. Description of Prior Art
In DE/AS 1 033 769, a rotor for a dynamo-electric machine is described in which its individual poles are attached to the core by dovetail projections.
From DE 42 13 377 A1, a brushless DC motor with internal rotor is known in which the stator is composed of L-shaped segments, said segments being inserted into a winding, said winding being spooled around a star-shaped body made of synthetic material.
In DE 44 36 257 A1, a salient pole rotor of a dynamo-electric machine is described that is made by pushing and clamping together two claw-shaped halves. The absence of every other pole in the rotor halves simplifies the direct spooling of the exciter poles which are executed in a layered sheet technique. All poles are symmetrically distributed over the circumference and identical.
Further, from DE 40 04 019 A1, stacked coils are known which, in spite of the slot width diminishing with the radius, make a high filling factor of the slot possible. The production of these stacked coils is very costly, and in order to mount said coils, open grooves are required which in turn cause pole face losses or expenditures for the production and assembly of soft magnetic groove retainer keys.
The objective of the present invention is, therefore, to advance an electric machine with a single pole winding and a process for its production in such a manner that, at a given size, losses are decreased and, at the same time, simple cost efficient production is possible.
According to the invention, this objective is achieved in accordance with the characteristics in the disclosure.
In accordance with the invention, the body constituting the individual poles is composed of soft magnetic segments which in turn consist of sheets that are stacked preferably in axial direction and that have grooves on those surfaces that constitute the wall of the slot, said grooves facilitating the exact tracking of the conductor wire when winding the exciter coils.
The first approach to achieve the objective is, therefore, to obtain a defined position of the windings by structuring the surface of the pole core and applying only thin insulation layers between the conductors and the pole core. This allows for good heat dissipation of the winding losses into the pole core and a high space factor in the slots.
In addition, round or profile wire spooled free of overlap in defined layers can be compacted into the desired shape by subsequent pressing. Beginning from an initial coil layer defined arranged by the grooves of the pole core, a precisely working winding machine can produce a reproducible coil surface, thereby creating the preconditions for the subsequent compaction and space saving assembly of the machine.
Complementary or alternatively, the second approach to achieving the objective of the invention, as described in claim 5, also allows good space utilization in multi-phase machines with single pole winding and, concurrently, results in a decrease of winding losses and of production costs. Here, the preferably annular soft magnetic body is composed of two segment designs that are alternately arranged in circumferential direction.
The pole pitch of the first segment designxe2x80x94hereinafter referred to as T-segmentxe2x80x94corresponds approximately to the pole pitch of the body that is arranged oppositely at the air gap. The pole pitch of the second segment designxe2x80x94hereinafter referred to as X-segmentxe2x80x94on the other hand, is smaller or larger by the fraction of the pole pitch that corresponds to the number of phases. The X-segment realizes the phase offset at the circumference of the successive T-segments and at the same time ensures a magnetically homogeneous air gap surface of the soft magnetic body. While the T-segment constitutes the coil core, the X-segment fills the space between two adjacent conductor coils and is preferably designed in such a manner that voids which increase heat resistance are avoided.
The coils may be spooled as wire coils preferably directly onto the T-segment or they may be prefabricated in a device as profile wire coils hardened by a bonding layer. The T-segment conducts magnetic flux predominantly in direction of the slot depth and may, therefore, be advantageously manufactured of grain-oriented material. On the other hand, the X-segment conducts flux also in direction of the slot width and, therefore, consists preferably of low-loss electric sheet without predominant grain direction.